1. Technical Field
The present invention relates to a magnetic resonance imaging apparatus for use in medical diagnosis systems. The invention also relates to a method of analyzing images provided by the imaging apparatus. More particularly, the invention is applied to a magnetic resonance imaging apparatus that is used to provide images of the coronary arteries.
2. Description of the Related Art
In recent years, image diagnosis apparatuses have advanced so much that the patient's heart can now be examined at the clinic site. In magnetic resonance imaging (MRI), for example, cine-scan, delayed enhancement imaging, stress myocardial perfusion imaging, and the like can now be performed. Although image diagnosis apparatuses have so advanced, the imaging of the coronary arteries cannot be so successfully achieved as desired. The images of the coronary arteries obtained are not as high in quality or stability as desired. This is not only because the coronary arteries are thin and run in a complex manner, but also because the heart moves in a complex way, too, and in a different manner from patient to patient. Hence, the coronary arteries must be imaged at high spatial resolution and high time resolution. To provide high-quality images of the coronary arteries, high skills are required in positioning the patient, setting various imaging conditions and inducing non-uniformity of the magnetic field.
Recently, methods of covering the entire heart in coronary artery MRI, using the balanced steady-state free precession (SSFP) sequence and respiratory navigator tracking, have been reported in, for example, Weber et al., Magnetic Resonance in Medicine, 50, 1223 1228, 2003, and Sakuma et al., Eizo joho MEDICAL, Vol. 36, No. 10.
In these methods, segmentation is performed, and the time of acquiring data for one heartbeat in ECG gating mode is as short as about 100 ms. The data-acquisition period must therefore be synchronized with the cardiac phase. Hitherto, to determine a cardiac phase in which the coronary arteries remains at rest, cardial cine scan should be performed before the coronary artery scan and the resulting cine images are carefully observed. It is important to observe both the image of the right coronary artery and the image of the left coronary artery.
In most cases, the right coronary artery and the left coronary artery differ in static phase and also in the duration of static phase. The operator therefore needs to observe the cine images very carefully. Thus, much time is required before imaging the coronary arteries. This is one of the factors that decrease examination throughput. The longer the examination lasts, the more tired the patient will be. Consequently, the cardiograph and respiration patterns become unstable, inevitably degrading image quality.